The determination of the retention curve of two different bentonites in conditions as close as possible to the actual clay barrier of a high level waste repository was the goal of this research. Two methods have been developed to determine the retention curve of the material for a fixed dry density. One of them involves the use of sulphuric acid solutions to control the relative humidity of the atmosphere in which the confined sample is placed. This method is time-consuming due to the slow equilibration of the clay at each suction value. For this reason, another method has been fine-tuned. It consists on the measurement, using a capacitive sensor, of the relative humidity of blocks of clay compacted to different dry densities and water contents. Theresults obtained with both methods are consistent. On the other hand, to better reproduce the actual conditions in the barrier, the two methods described above have been adapted to use them at different temperatures. The first method is being used up to 80 deg C, whereas the second one has properly worked up to 100 deg C.
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